Method of forming MOSFET structure

ABSTRACT

A method of forming a MOSFET structure is provided. In the method, an epitaxial layer is formed. A cap layer is formed above the epitaxial layer. A first trench is formed above the epitaxial layer. A protection layer is deposited within the first trench. The protection layer is a material selected from the group consisting of germanium and silicon-germanium.

FIELD

This disclosure relates to semiconductor technology, and moreparticularly, a method of forming a MOSFET structure.

BACKGROUND

During formation of a FinFET structure, a source/drain portion includinga cap layer and an epitaxial layer may be hurt by several etchingprocesses. If the source/drain portion is hurt, after a gate metal layeris formed within the FinFET structure, a silicon fin of the FinFETstructure may be in direct contact with an epitaxial silicon definitionlayer of the Fin structure. Therefore, leakage of the gate metal layermay be introduced, and operation failure may occur because of theleakage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 illustrate cross-sectional views of a FinFET structure duringformation of the FinFET structure.

FIGS. 6-14 illustrate cross-sectional views of a FinFET structure duringformation of the FinFET structure according to a first embodiment.

FIGS. 15-17 illustrate cross-sectional views of a FinFET structureduring formation of the FinFET structure according to a secondembodiment.

FIG. 18 illustrates a flowchart of a method of forming a MOSFETstructure.

DETAILED DESCRIPTION

FIGS. 1-5 illustrate cross-sectional views of a FinFET structure 100during formation of the FinFET structure 100.

In FIG. 1, the FinFET structure 100 initially includes a firstphotoresist layer 110, a second photoresist layer 120, an inter-layerdielectric (ILD) layer 130, a bottom photoresist layer 140, a gate layer160, a substrate layer 150, a cap layer 170, and an epitaxial layer 180.A source/drain portion of the FinFET structure 100 includes the caplayer 170 and the epitaxial layer 180. A tri-layer photoresist techniquemay be employed to form the first photoresist layer 110, the secondphotoresist layer 120 and the bottom photoresist layer 140, wherein thefirst photoresist layer 110 may be formed of a mixture of a photoresistmaterial and silicon, the second photoresist layer 120 may be formed ofa photoresist material, and the bottom photoresist layer 140 may beformed of polymer. The term “bottom” of the bottom photoresist layer 140refers to a relative position with respect to the first photoresistlayer 110 and the second photoresist layer 120, and does not limitscopes of the claims.

The gate layer 160 may include three exemplary gate portions, includinga first gate 165, a second gate 175, and a third gate 185. The firstgate 165 includes a first metal portion 166, a first gate ceiling 167, afirst gate bottom 171, a first left-side spacer 168, and a firstright-side spacer 169. The second gate 175 includes a second metalportion 176, a second gate ceiling 177, a second gate bottom 181, asecond left-side spacer 178, and a second right-side spacer 179. Thethird gate 185 includes a third metal portion 186, a third gate ceiling187, a third gate bottom 191, a third left-side spacer 188, and a thirdright-side spacer 189.

The first gate ceiling 167, the second gate ceiling 177, and the thirdgate ceiling 187 may consist essentially of silicon nitride.

The FinFET structure 100 may further include a shallow trench isolation(STI) layer 195 for isolation. The STI layer 195 is interposed betweenthe first gate 165 and the second gate 175.

In FIG. 2, a first etching process is performed. The second photoresistlayer 120 is substantially etched. Part of the first photoresist layer110 and part of the bottom photoresist layer 140 are also substantiallyetched following a pattern of the second photoresist layer 120 forforming a first trench 210. Part of the ILD layer 130 is exposed in thefirst etching process.

An etchant utilized in the first etching process may have a highselectivity with the ILD layer 130.

In FIG. 3, a second etching process is performed. The first photoresistlayer 110 is substantially etched. Part of the bottom photoresist layer140 within the first trench 210 and the cap layer 170 are substantiallyetched to form a second trench 310. An exposed portion of the ILD layer130 is substantially etched. An etchant used in the second etchingprocess may have a similar selectivity with the ILD layer 130, thebottom photoresist layer 140, and the second gate ceiling.

As can be observed in FIG. 3, since the cap layer 170 is substantiallyetched, the epitaxial layer 180 is not substantially covered andprotected by the cap layer 170 in the following processes.

In FIG. 4, a third etching process is performed. The second gate ceilingand part of the second right-side spacer protecting the second gateceiling are substantially etched. An etchant used in the third etchingprocess may have a high selectivity with the ILD layer 130 and theepitaxial layer 180.

In FIG. 5, a fourth etching process is performed. The bottom photoresistlayer 140 previously above the ILD layer 130 is substantially etched. Anetchant used in the fourth etching process may have a high selectivitywith the ILD layer 130 and the epitaxial layer 180.

Since the epitaxial layer 180 is exposed since the second etchingprocess, the epitaxial layer 180 may be significantly damaged infollowing process. As a result, it may affect operations of the FinFETstructure 100.

FIGS. 6-14 illustrate cross-sectional views of a FinFET structure 600during formation of the FinFET structure 600 according to a firstembodiment.

In FIG. 6, the FinFET structure 600 initially includes an inter-layerdielectric (ILD) layer 630, a gate layer 660, a substrate layer 650, acap layer 670, and an epitaxial layer 680. A source/drain portion of theFinFET structure 600 includes the cap layer 670 and the epitaxial layer680. A first trench 690 is formed by patterning the ILD layer 630, andis above the cap layer 670 and the epitaxial layer 680.

In one example, the cap layer 670 may consist essentially of silicon,and the epitaxial layer 680 may consist essentially ofsilicon-germanium.

The gate layer 660 may include three exemplary gate portions, includinga first gate 665, a second gate 675, and a third gate 685. The firstgate 665 includes a first metal portion 666, a first gate ceiling 667, afirst gate bottom 671, a first left-side spacer 668, and a firstright-side spacer 669. The second gate 675 includes a second metalportion 676, a second gate ceiling 677, a second gate bottom 681, asecond left-side spacer 678, and a second right-side spacer 679. Thethird gate 685 includes a third metal portion 686, a third gate ceiling687, a third gate bottom 691, a third left-side spacer 688, and a thirdright-side spacer 689.

The first gate ceiling 667, the second gate ceiling 677, and the thirdgate ceiling 687 may consist essentially of silicon nitride.

The FinFET structure 600 may further include a STI layer 695 forisolation. The STI layer 695 is interposed between the first gate 665and the second gate 675.

In FIG. 7 a protection layer 710 is formed within the first trench 690for protecting the cap layer 670 and the epitaxial layer 680. In someexamples, a material of the protection layer 710 may be germanium orsilicon-germanium, so that the protection layer 710 is capable ofwithstanding some following-mentioned etching processes.

In an example, the protection layer 710 may protrude out of the trench690. In FIG. 8, an additional chemical-mechanical polishing (CMP) may beutilized for planarizing a protruding portion of the protection layer690.

In FIG. 9, a bottom photoresist layer 940 is formed above the protectionlayer 710 and the ILD layer 630. A first photoresist layer 910 is formedabove the bottom photoresist layer 940. A second photoresist layer 920is formed above the first photoresist layer 910.

In one example, the first photoresist layer 910 may consist essentiallyof silicon and PR mixture.

In FIG. 10, a first etching process is performed. The second photoresistlayer 920 is substantially etched to pattern the bottom photoresistlayer 940 and the first photoresist layer 910 for forming a secondtrench 1010. A first portion of the ILD layer 630 and a first portion ofthe protection layer 710 may be in direct contact with the second trench1010.

In one example, an etchant used in the first etching process may have ahigh selectivity with the ILD layer 630. In another example, the etchantused in the first etching process may be gas selected from the groupconsisting of N₂/H₂-mixed gas, O₂ gas, CO₂ gas, CO gas, SO₂ gas, andetc.

In FIG. 11, a second etching process is performed. The first photoresistlayer 910, part of the ILD layer 630, and part of the protection layer710 are substantially etched to form a third trench 1110. A secondportion of the protection layer 710 may be in direct contact with thethird trench 1110.

In one example, an etchant used in the second etching process may beCF₄/CHF₃-mixed gas.

In FIG. 12, a third etching process is performed. The bottom photoresistlayer 940 is substantially etched.

In one example, an etchant used in the third etching process is O₂ gas,or N₂/H₂-mixed gas, CO₂ gas, CO gas, SO₂ gas, and etc.

In FIG. 13, a fourth etching process is performed. The protection layer710 is substantially etched to form a fourth trench 1310.

In a first example, the fourth etching process is a dry etching process.

In a second example, the fourth etching process is a wet etchingprocess.

In a third example, an etchant used in the fourth etching process issulfuric peroxide mixture (SPM).

In a fourth example, the etchant used in the fourth etching process isammonia peroxide mixture (APM).

In FIG. 14, a fifth etching process is performed. Part of the first gateceiling and the second gate ceiling are removed.

Since the cap layer 670 is protected by sacrificing the protection layer710, the epitaxial layer 680 can still be protected by the protectionlayer 670. As a result, the epitaxial layer 680 can be alleviated frombeing damaged in following processes, and operational accuracy of theFinFET structure 600 can be preserved.

FIGS. 15-17 illustrate cross-sectional views of a FinFET structure 1500during formation of the FinFET structure 1500 according to a secondembodiment.

In FIG. 15, the FinFET structure 1500 initially includes an ILD layer1530, a gate layer 1560, a substrate layer 1550, a cap layer 1570, andan epitaxial layer 1580. A source/drain portion of the FinFET structure1500 includes the cap layer 1570 and the epitaxial layer 1580. A firsttrench 1594 is formed by patterning the ILD layer 1530, and is above thecap layer 1570 and the epitaxial layer 1580.

The gate layer 1560 may include three exemplary gate portions, includinga first gate 1565, a second gate 1575, and a third gate 1585.

The FinFET structure 1500 may further include a STI layer 1595 forisolation. The STI layer 1595 is interposed between the first gate 1565and the second gate 1575.

Unlike forming a protruding protection layer 710 in FIG. 7, aconcave-topped protection layer 1597 is formed within the first trench1594, as shown in FIG. 15.

In FIG. 16, an bottom photoresist layer 1640 is formed above theprotection layer 1597 and the ILD layer 1530. A first photoresist layer1610 is formed above the bottom photoresist layer 1640. A secondphotoresist layer 1620 is formed above the first photoresist layer 1610.

In FIG. 17, the second photoresist layer 1620 is substantially etched topattern the bottom photoresist layer 1640 and the first photoresistlayer 1610 for forming a second trench 1710.

After substantially etching the first photoresist layer 1610, part ofthe ILD layer 1530, and part of the protection layer 1597, the formationof the FinFET structure 1500 will be the same as shown in FIG. 12. Thefollowing processes to be performed on the FinFET structure 1500 arealso the same as shown in FIGS. 13-14.

Therefore, the FinFET structure 1500 may also alleviate the epitaxiallayer 1580 from being damaged in processes before the completion offorming the FinFET structure 1500.

FIG. 18 illustrates a flowchart of a method of forming a MOSFETstructure. The method includes the following stages: forming anepitaxial layer (1802); forming a cap layer above the epitaxial layer(1804); forming a first trench above the epitaxial layer (1806);depositing a protection layer within the first trench (1808); forming abottom photoresist layer above the protection layer and the ILD layer(1810); forming a first photoresist layer above the bottom photoresistlayer (1812); forming a second photoresist layer above the firstphotoresist layer (1814); substantially etching the second photoresistlayer to pattern the bottom photoresist layer and the first photoresistlayer for forming a second trench (1816); substantially etching thefirst photoresist layer, the first portion of the ILD layer, and thefirst portion of the protection layer to form a third trench (1818);substantially etching the bottom photoresist layer (1820). Substantiallyetch the second portion of the protection layer (1822).

This disclosure teaches a method of forming a MOSFET structure. In themethod, an epitaxial layer is formed. A cap layer is formed above theepitaxial layer. A first trench is formed above the epitaxial layer. Aprotection layer is deposited within the first trench. The protectionlayer is a material selected from the group consisting of germanium andsilicon-germanium.

This disclosure also teaches a MOSFET structure. The MOSFET structureincludes an epitaxial layer, a cap layer, and a protection layer. Thecap layer is formed above the epitaxial layer. The protection layer isdeposited within a first trench of the MOSFET structure above theepitaxial layer. The protection layer is a material selected from thegroup consisting of germanium and silicon-germanium.

This disclosure also teaches another method of forming a MOSFETstructure. In this method, an epitaxial layer is formed. A cap layer isformed above the epitaxial layer. An ILD layer of the MOSFET structureis patterned to form a first trench above the epitaxial layer. Aprotection layer is deposited within the first trench. An bottomphotoresist layer is formed above the protection layer and the ILDlayer. A first photoresist layer is formed above the bottom photoresistlayer. A second photoresist layer is formed above the first photoresistlayer. The protection layer is a material selected from the groupconsisting of germanium and silicon-germanium.

This written description uses examples to disclose embodiments of thedisclosure, include the best mode, and also to enable a person ofordinary skill in the art to make and use various embodiments of thedisclosure. The patentable scope of the disclosure may include otherexamples that occur to those of ordinary skill in the art. One ofordinary skill in the relevant art will recognize that the variousembodiments may be practiced without one or more of the specificdetails, or with other replacement and/or additional methods, materials,or components. Well-known structures, materials, or operations may notbe shown or described in detail to avoid obscuring aspects of variousembodiments of the disclosure. Various embodiments shown in the figuresare illustrative example representations and are not necessarily drawnto scale. Particular features, structures, materials, or characteristicsmay be combined in any suitable manner in one or more embodiments.Various additional layers and/or structures may be included and/ordescribed features may be omitted in other embodiments. Variousoperations may be described as multiple discrete operations in turn, ina manner that is most helpful in understanding the disclosure. However,the order of description should not be construed as to imply that theseoperations are necessarily order dependent. In particular, theseoperations need not be performed in the order of presentation.Operations described herein may be performed in a different order, inseries or in parallel, than the described embodiments. Variousadditional operations may be performed and/or described. Operations maybe omitted in additional embodiments.

This written description and the following claims may include terms,such as left, right, top, bottom, over, under, upper, lower, first,second, etc. that are used for descriptive purposes only and are not tobe construed as limiting. For example, terms designating relativevertical position may refer to a situation where a device side (oractive surface) of a substrate or integrated circuit is the “top”surface of that substrate; the substrate may actually be in anyorientation so that a “top” side of a substrate may be lower than the“bottom” side in a standard terrestrial frame of reference and may stillfall within the meaning of the term “top.” The term “on” as used herein(including in the claims) may not indicate that a first layer “on” asecond layer is directly on and in immediate contact with the secondlayer unless such is specifically stated; there may be a third layer orother structure between the first layer and the second layer on thefirst layer. As an example, the structures, layouts, materials,operations, voltage levels, or current levels related to “source” and“drain” described herein (including in the claims) may beinterchangeable as a result of transistors with “source” and “drain”being symmetrical devices. The term “substrate” may refer to anyconstruction comprising one or more semiconductive materials, including,but not limited to, bulk semiconductive materials such as asemiconductive wafer (either alone or in assemblies comprising othermaterials thereon), and semiconductive material layers (either alone orin assemblies comprising other materials). The embodiments of a deviceor article described herein can be manufactured, used, or shipped in anumber of positions and orientations. Persons skilled in the art willrecognize various equivalent combinations and substitutions for variouscomponents shown in the figures.

What is claimed is:
 1. A method of forming a MOSFET structure, comprising: forming an epitaxial layer; forming a cap layer above the epitaxial layer; forming a first trench above the epitaxial layer, wherein the forming the first trench above the epitaxial layer comprises patterning an inter-layer dielectric (ILD) layer of the MOSFET structure to form the first trench; depositing a protection layer within the first trench; and forming a bottom photoresist layer above the protection layer and the ILD layer; forming a first photoresist layer above the bottom photoresist layer; and forming a second photoresist layer above the first photoresist layer, wherein the protection layer is a material selected from the group consisting of germanium and silicon-germanium.
 2. The method of claim 1, further comprising: performing a chemical mechanical polishing (CMP) process on the protection layer.
 3. The method of claim 1, further comprising: substantially etching the second photoresist layer to pattern the bottom photoresist layer and the first photoresist layer for forming a second trench.
 4. The method of claim 3, wherein the substantially etching the second photoresist layer to pattern the bottom photoresist layer and the first photoresist layer for forming the second trench comprises substantially etching the second photoresist layer to pattern the bottom photoresist layer and the first photoresist layer for forming the second trench using gas selected from the group consisting of N₂/H₂-mixed gas, O₂ gas, and CO₂ gas.
 5. The method of claim 3, further comprising: substantially etching the first photoresist layer, the first portion of the ILD layer, and the first portion of the protection layer to form a third trench.
 6. The method of claim 5, wherein the substantially etching the first photoresist layer, the first portion of the ILD layer, and the first portion of the protection layer to form the third trench comprises substantially etching the first photoresist layer, the first portion of the ILD layer, and the first portion of the protection layer to form the third trench using CF₄/CHF₃-mixed gas.
 7. The method of claim 5, further comprising: substantially etching the bottom photoresist layer.
 8. The method of claim 7, wherein the substantially etching the bottom photoresist layer comprises substantially etching the bottom photoresist layer using O₂ gas, or N₂/H₂-mixed gas, CO₂ gas, CO gas, SO₂ gas, and etc.
 9. The method of claim 7, further comprising: substantially etching the second portion of the protection layer.
 10. The method of claim 9, wherein the substantially etching the second portion of the protection layer comprises substantially etching the second portion of the protection layer using dry etching.
 11. The method of claim 9, wherein the substantially etching the second portion of the protection layer comprises substantially etching the second portion of the protection layer using wet etching.
 12. The method of claim 9, wherein the substantially etching the second portion of the protection layer comprises substantially etching the second portion of the protection layer using a sulfuric peroxide mixture (SPM).
 13. The method of claim 9, wherein the substantially etching the second portion of the protection layer using an ammonia peroxide mixture (APM).
 14. A method of forming a MOSFET structure, comprising: forming an epitaxial layer; forming a cap layer above the epitaxial layer; patterning an inter-layer dielectric (ILD) layer of the MOSFET structure to form a first trench above the epitaxial layer; depositing a protection layer within the first trench; forming a bottom photoresist layer above the protection layer and the ILD layer; forming a first photoresist layer above the bottom photoresist layer; and forming a second photoresist layer above the first photoresist layer, wherein the protection layer is a material selected from the group consisting of germanium and silicon-germanium.
 15. A method of forming a MOSFET structure, comprising: forming an epitaxial layer; forming a cap layer above the epitaxial layer; patterning an inter-layer dielectric (ILD) layer of the MOSFET structure to form a first trench above the epitaxial layer; depositing a concave-topped protection layer within the first trench; forming a bottom photoresist layer above the protection layer and the ILD layer; forming a first photoresist layer above the bottom photoresist layer; forming a second photoresist layer above the first photoresist layer; and substantially etching the second photoresist layer to pattern the bottom photoresist layer and the first photoresist layer for forming a second trench.
 16. The method of claim 15, wherein depositing the concave-topped protection layer within the first trench further comprises depositing the concave-topped protection layer by using a material selected from the group consisting of germanium and silicon-germanium. 